(1) Field of the Invention
The present invention relates to electronic circuits. More specifically, the present invention relates to a circuit interfacing between a computer system and a network.
(2) Description of the Related Art
Typically, network controllers are used to carry out conversion and transfer between ordinary payload data (residing in a system memory of a computer system) and frames transmitted to or received from a network upstream or downstream. One such network controller may be an Intel Pro 100-A Fast Ethernet controller (including a Media Access Control Circuit (Big MAC) that has a part number 202513-302) made by Intel Corporation of Santa Clara, Calif. An Ethernet controller carries out the above-mentioned conversion and transfer of data, producing Ethernet frames that may be transmitted upstream at frequencies different than the frequency at which the Ethernet controller typically operates. The Ethernet controller also handles frames transmitted thereto downstream at frequencies different than the frequency at which the Ethernet controller operates.
A serial downstream rate at which data packets may be transmitted to an Ethernet controller may be 30 Megabits/second (MB/s), while a serial upstream rate at which data packets may be transmitted to the network may be 128 kilobits/second (KB/s). These rates are subject to change depending on the modulation technology and frequency bandwidth used. Since the downstream transmission rate exceeds 10 MB/s, an ordinary 10 MB/s Ethernet controller may not be adequate for this type of application. While more advanced Ethernet controllers are switch selectable, to operate at either 100 MB/s or 10 MB/s, they do not provide the flexibility for transmitting data upstream or receiving data downstream at frequencies other than 10 MB/s or 100 MB/s. If the downstream or upstream frequencies are different from the frequency at which the Ethernet controller operates, data may be lost in the process of transmission or receipt. Additionally, some Ethernet controllers, including the Big MAC, typically transmit or receive data in parallel, i.e., transmit or receive a nibble of data (four bits) at one time, although data is transmitted to or received from the network in serial form.
It is desirable to provide a circuit that interfaces between a network controller and a network that permits conversion of data from parallel to serial format and vice versa. It is also desirable to provide a circuit that interfaces between a network and a network controller that transfers data to or from the network controller from or to a network, where the frequencies at which data is transmitted to or received from the network differ from the frequency at which the network controller operates.